1. Field of the Invention
The present invention is related generally to detectors for use in liquid chromatography, and more particularly to an on-column detector utilizing variations in intensity of scattered light in the column arising from variations in the eluent refractive index as the eluent passes through the column.
2. Description of Related Art
Flash and gravity-fed chromatography are simple, commonly used preparative techniques for the separation of liquids, such as might be found in chemical reaction mixtures. A hollow column is packed with a solid particulate material, and a liquid eluent containing two or more components is caused to flow through the column. Gravity and/or compressed air may be used to enhance the flow rate. As the solution flows through the column, the components are differentially adsorbed onto and released from the particle surfaces, resulting in separation of the components from each other. Different volume fractions of the eluent can be collected after they exit the column, with each volume fraction enriched in one or more components and depleted in the other components relative to the eluent that enters the column.
The particulate packing material is selected to have different binding affinities for the solvent and the different dissolved species. Common packing materials include particles of silica gel or alumina. A typical particle size for silica gel is 60-200 mesh, or 75-250 xcexcm diameter.
Frequently, glass columns are used for flash chromatography. The glass column containing the packing material allows for visualization of colored compounds as they are eluted from the column. However, because most separations involve non-colored compounds, products are typically isolated by collecting numerous fractions after the eluent exits the column and analyzing the fractions. Post-column analysis usually involves tedious evaluation of often more than a dozen fractions by thin layer chromatography.
It is an object of the present invention to provide an apparatus and method for monitoring a chromatography column to provide the operator with the information necessary to collect only eluent fractions that contain compounds of interest.
It is another object of the present invention to provide an easily portable apparatus for monitoring a chromatography column.
It is yet another object of the present invention to provide an apparatus and method for monitoring a chromatography column wherein the apparatus and method are useful with a wide range of compounds, including compounds that are substantially non-absorbing over the range of visible wavelengths.
It is still another object of the present invention to provide an apparatus and method for monitoring a chromatography column that are useful over a wide range of separation conditions. It is a further object of the present invention to provide an apparatus and method for monitoring a chromatography column that are useful over a wide range of column sizes.
It is yet a furher object of the present invention to provide an apparatus and method for monitoring a chromatography column that is inexpensive to construct.
It is still a further object of the present invention to provide an apparatus and method for monitoring a chromatography column that is simple to use.
To achieve the foregoing and other objects and in accordance with the purpose of the present invention broadly described herein, one embodiment of this invention comprises an apparatus for detecting liquids in a chromatography column which contains a stationary solid chromatography packing material and a liquid eluent. The apparatus comprises a light source positioned adjacent to the column and a light detector positioned adjacent to the column. The detector is substantially coplanar with and spaced apart radially from the light source, and the detector is responsive to changes in the intensity of light emanating from the source and scattered by the packing material in the column. The changes in light intensity may be caused by changes in the refractive index of the liquid eluent. The source and detector may be positioned at substantially the same height on the column and spaced apart radially at an angle between about 0 and about 180 degrees, preferably between about 90 and about 180 degrees. The light emanating from the source is substantially monochromatic, and the detector is capable of detecting light at the wavelength produced by the source. Preferably, the light source is a laser, and the detector is a photodiode. The apparatus is suitable for use with forms of liquid chromatograpy where the packing material scatters light. The apparatus is particularly suitable for use in monitoring flash chromatography and gravity-fed chromatograpy. Multiple detectors may be used with a single light source, spaced apart radially from each other. Also, one or more additional combinations of a light source and a detector may be positioned along the column.
Another embodiment of the present invention comprises an apparatus for detecting fluids in a chromatography column which contains a stationary solid chromatography packing material and a liquid eluent. The apparatus comprises a light source positioned adjacent to the column and a means for detecting variations in light scattered by the packing material as the fluid solution passes through the column. The amount of light scattered depends upon the difference between the refractive index of an eluent and the packing material. Preferably, the means for detecting light variations is a photodiode detector. The apparatus may also comprise means for collecting and storing data relating to the detected variations in light, such as an analog-to-digital converter and a microprocessor or a computer. In addition, some light variations may be due to light absorption by the eluent.
In yet another embodiment, the present invention comprises a method for detecting the presence of a liquid eluent in a chromatography column containing a stationary solid particulate chromatography packing material. The method comprises measuring the variations in the intensity of light scattered by the packing material. The variations in light intensity may be caused by variations in the refractive index of the eluent. The variations in light intensity may be measured using a light source and a detector positioned adjacent to the column, and the light source and the detector are spaced apart radially from each other, and the source and the detector may be moved longitudinally along the column to monitor progress of the eluent inside the column. Measurements may be made at a plurality of locations adjacent to the column, possibly using multiple light sources and detectors spaced along the column, with each detector spaced apart radially from a light source. The method may comprise the additional step of monitoring variations in the intensity of the scattered light over a time interval. The light should be substantially monochromatic and, preferably, the liquid, the column, and the packing material are substantially transparent to light at the wavelength produced by the source. Also preferably, the light has a wavelength in the visible range.